This invention relates in general to infinitely variable ratio transmission drive systems and in particular to such systems which incorporate as the connecting means between the driving and driven discs a continuous length of transmission drive chain.
The concept of infinitely variable ratio transmission drive systems is well known in the art. Such systems involve the placement of two pairs of conical discs on two parallel shafts. The separation between each pair of discs on each shaft is able to be changed such that the connecting drive member (belts or chains) which extends around these pairs of discs will act upon the discs at a different drive radius location. Consequently, if it is desired to step down from a large radius on the input shaft to a small radius on the output shaft, the driving discs are placed close together and the driven discs are placed farther apart. The use of conical shaped discs as the driving and driven members, which are movable to any degree of separation along the two parallel shafts, creates the infinitely variable ratio aspect for the transmission drive system.
Typically, the connecting member is a belt, such as a V-belt whose sides are correspondingly tapered to conform to the driving and driven discs and frictional contact between these tapered sides and the discs is relied upon to transmit and convert input torque at a certain RPM to output torque at a different RPM. Similarly, the discs may be radially grooved and the belts may then include outwardly extending protrusions for a direct drive system. One disadvantage with the use of V-belts is that they are normally constructed from a soft, flexible material and may only be subjected to comparatively low compression forces. Consequently, they must be of an increased size in order to provide sufficient surface area of contact with the discs to provide sufficient friction. This condition results in large diameters to the discs and increases the overall size and weight of the transmission system. There are also other considerations such as the life and durability of the connecting member as well as the speed at which it can be operated.
An awareness of these various drawbacks have led certain inventors to the conclusion that replacement of the synthetic belt material by metal constitutes an improvement to the overall transmission system. Correspondingly, there have been a number of attempts at the utilization of a metal chain as the connecting member between the driving and driven discs. Although this concept overcomes certain disadvantages with the use of V-belts, a number of additional problems have been introduced. Due to the fact that conventional roller chain design is not compatible with the requirements of infinitely variable ratio transmission drive systems, special types of chains have resulted. In order to provide high strength, reliability, prolonged life and sufficient frictional forces, each of the chain concepts which have been conceived have resulted in a quite complex and intricate aggregation of parts. In certain instances the assembly of such chains is extremely complex and the corresponding costs quite high. In other situations where the particular concept is somewhat more basic, the chain does not provide all the necessary attributes that such a chain drive must have in order to be suitable for the variable ratio transmission concepts.
Listed below are several patent references which disclose certain concepts for variable ratio transmission drives and certain chain concepts for use with such drives.
______________________________________ U.S. PAT. NO. PATENTEE ISSUE DATE ______________________________________ 2,073,846 Maurer 03/16/37 2,550,431 Shaw 04/24/51 2,913,916 Schmidt 11/24/59 1,814,883 Abbott 07/14/31 1,966,831 Oakes et al. 07/17/34 1,501,705 Decoux 07/15/24 1,662,654 Abbott 03/13/28 2,894,405 Carle 07/14/59 3,016,756 Jackel 01/16/62 3,718,405 Keiter et al. 02/27/73 3,906,809 Erickson 09/23/75 ______________________________________
Maurer discloses a wedge shaped power transmitting member and system which includes a plurality of disc engaging elements constructed of hardened steel or similar material which are disposed transversely in each chain link and provide a curved surface of contact against the corresponding driving and driven discs. In the various disclosed embodiments the engaging elements are rollers and are arranged such that they may move along the inclined surface of the various discs while providing a frictional surface for transmitting drive motion.
Shaw discloses a variable-speed transmission chain concept wherein the chain is made up of links and pins in a manner similar to conventional power transmitting chains. However, this particular design differs in that the pins extend well beyond the sides of the links and the ends of the pins are conical thereby provding a line contract bearing against the inclined surfaces of the discs in order to create the necessary frictional interface for transmission from input to output.
Schmidt discloses a stepless change speed transmission system wherein a first pair of axially adjustable gear-like toothed conical members are connected to an incoming power shaft and a second pair of axially adjustable gear-like toothed conical members are connected to an outgoing power shaft and a chain having teeth-like elements capable of meshing with the teeth of the conical members is in operative engagement with the various pairs of conical members.
Abbott ('883) discloses a power transmission mechanism of a type similar to Schmidt except that the portions which engage the teeth-like portions of the conical members (discs) are constructed of a plurality of laminations which extend completely through the plurality of link plates.
Oakes et al. discloses a variable speed transmission system which incorporates a pair of facing conical members which are movable one with respect to the other by means of a threaded rod and linkage arrangement. A chain drive concept is disclosed which includes outwardly extending portions from each link which engage the grooves in the conical members.
Decoux discloses a power transmission apparatus operated by means of a flexible member such as a belt wherein the variation of the speed of the power transmissions is effected by varying the operative diameter of one pulley or both pulleys by changing the spacing between facing inwardly tapering conical disc members.
Abbott ('654) discloses an expanding pulley concept in combination with a chain drive for use in transmission systems.
Carle discloses a variable speed transmission which is intended to incorporate an improved belt and pulley arrangement in order to provide variable speed belt transmission in which the limitations imposed by belt slippage are materially reduced. A composite endless belt is provided which has different inner and outer driving surface portions each constructed of different material. One presents a smooth friction drive and the other presents a positive drive.
Jackel discloses a metal reinforced V-shaped belt which is intended to have improved longitudinal strength and is adapted to withstand high lateral forces. The end use for such a belt is intended to be with variable speed drives and adjustable width pulleys of the type used with variable ratio transmission systems.
Keiter et al. discloses a variable speed pulley drive transmission system for overarm machine tools such as drill presses. Although movable conical discs are provided as the transmission means, the connecting means is of a conventional belt design and the patent focuses primarily on the operator controls which permit the variable speed conversion.
Erickson discloses a transmission having an infinitely variable drive ratio wherein a pair of oppositely oriented adjacent splined cone shaped members are interconnected by a selectively positional positive gripping drive chain. The links of the chain are contoured so as to fit over and within the splined protrusions of each cone shaped member.
While the various disadvantages with synthetic (rubber) belt drives are readily apparent as has been mentioned, there are also disadvantages with all-metal chain drive concepts. These disadvantages are seen from the standpoint of cost, complexity and the amount of frictional interference which is provided. At least one attempt has been made to create a V-belt profile from steel in which a plurality of individual steel blocks are connected together by a steel band in much the same manner that link chain is constructed with hopefully improvements from the standpoint of cost and durability. One such attempt has been made by Van Doorne Transmissive BV as set forth in an article entitled "DAF Transmatic Uses Steel Belts for Drive" printed in the Automotive News of Feb. 23, 1976. The particular belt developed includes a thin steel band which carries a set of steel blocks each with a V-belt profile. These individual steel blocks fit into pulley grooves and rely on frictional interference for transmission drive.
Although chain drive concepts do provide certain advantages over the use of synthetic V-belts, chain drives also have their own associated problems. Since chain drives are normally utilized to increase the driving speed and the amount of force, they may be subjected to great stresses in a variety of directions with constant forces as well as variable forces. Such stress forces primarily align themselves along the length of the chain as torque is transferred from the imput shaft to the output shaft. These stress forces aligned along the chain result in both shear stresses introduced into the connecting pins as well as severe bending moments. Often chain fatigue and failure results from pin tear out in the link plate holes which is often the result of severe bending moments in the pins which apply pressure at these locations. High stress forces on the pins may tend to elongate or otherwise distort the link plate holes until the fit is so loose that the pins pull out. Consequently, it would be an improvement to such chain designs if means could be provided in a convenient, economical and easily assembled manner to either eliminate or greatly reduce certain of these forces. Reduced forces in turn reduce any adverse effects on the connecting pins and link plates such that great strength and speed can be transmitted while still providing greater chain durability, strength and prolonged life.
The subject invention which is disclosed and described hereinafter achieves these improvements while providing additional advantages and benefits which will be apparent from the following descriptions.